Photonic coupler

Abstract

A photonic coupler includes an input coupling section, an output coupling section, and a multimode interference (MMI) waveguide section. The input coupling section is adapted to receive an input optical signal along an input waveguide channel. The output coupling section is adapted to output a pair of output optical signals along output waveguide channels. The output optical signals having output optical powers split from the input optical signal. The MMI waveguide section is optically coupled between the input and output coupling sections. Notched waveguide sections may each be disposed between the MMI waveguide section and a corresponding one of the input or output coupling sections and/or the MMI waveguide section may include curvilinear sidewalls.

What is claimed is: 
     
       1. A photonic combiner, comprising:
 an input coupling section adapted to receive input optical signals along input waveguide channels; 
 an output coupling section adapted to output an output optical signal along an output waveguide channel, the output optical signal having an output optical power from combining the input optical signals; 
 a multimode interference (MMI) waveguide section optically coupled between the input and output coupling sections; and 
 notched waveguide sections including a first notched waveguide section disposed between the MMI waveguide section and the input coupling section and a second notched waveguide section disposed between the MMI waveguide section and the output coupling section, wherein the notched waveguide sections each including a pair of opposing sidewall notches that expands and contracts a lateral cross-section of a corresponding one of the notched waveguide sections along a longitudinal axis of the photonic combiner. 
 
     
     
       2. The photonic combiner of  claim 1 , wherein the photonic combiner comprises a 2×2 photonic combiner having a pair of output waveguide channels including the output waveguide channel. 
     
     
       3. The photonic combiner of  claim 2 , wherein the notched waveguide sections are each disposed proximate to a juncture of either the input waveguide channels or the output waveguide channels. 
     
     
       4. The photonic combiner of  claim 1 , wherein the MMI waveguide section includes curvilinear sidewalls each having a smooth uninterrupted curvature extending between the notched waveguide sections. 
     
     
       5. The photonic combiner of  claim 4 , wherein the curvilinear sidewalls arc inwards towards a central region of the MMI waveguide section forming a smooth and gradual narrowing of the MMI waveguide at the central region. 
     
     
       6. The photonic combiner of  claim 4 , wherein a lateral cross-section of the MMI waveguide section is narrower at a longitudinal center of the MMI waveguide section than longitudinal peripheries of the MMI waveguide section. 
     
     
       7. The photonic combiner of  claim 1 , further comprising:
 sidewall corrugations disposed along the input waveguide channels and the output waveguide channel. 
 
     
     
       8. The photonic combiner of  claim 7 , wherein the sidewall corrugations comprise opposing pairs of sidewall corrugations on each of the input waveguide channels and the output waveguide channel. 
     
     
       9. The photonic combiner of  claim 1 , wherein the photonic combiner comprises a planar waveguide disposed within a semiconductor material surrounded by semiconductor oxide material. 
     
     
       10. The photonic combiner of  claim 1 , wherein the input waveguide channels and the output waveguide channel are single mode waveguides. 
     
     
       11. The photonic combiner of  claim 1 , wherein the MMI waveguide section and the notched waveguide sections are symmetrical about a lateral axis passing through a center of the MMI waveguide section. 
     
     
       12. A photonic coupler, comprising:
 an input coupling section adapted to receive input optical signals along input waveguide channels; 
 an output coupling section adapted to output an output optical signal along an output waveguide channel, the output optical signal having an output optical power from combining the input optical signals; and 
 a multimode interference (MMI) waveguide section optically coupled between the input and output coupling sections, wherein the MMI waveguide section includes curvilinear sidewalls that arc inwards towards a central region of the MMI waveguide section, wherein the curvilinear sidewalls of the MMI waveguide section each have a single smooth uninterrupted curvature that extends an entire length of the MMI waveguide section. 
 
     
     
       13. The photonic coupler of  claim 12 , wherein the photonic coupler comprises a 2×2 photonic coupler having a pair of output waveguide channels including the output waveguide channel. 
     
     
       14. The photonic coupler of  claim 13 , further comprising:
 notched waveguide sections each disposed between the MMI waveguide section and a corresponding one of the input or output coupling sections, the notched waveguide sections each including a pair of opposing sidewall notches that expands and contracts a lateral cross-section of a corresponding one of the notched waveguide sections along a longitudinal axis of the photonic coupler. 
 
     
     
       15. The photonic coupler of  claim 14 , wherein the notched waveguide sections are each disposed proximate to a juncture of either the input waveguide channels or the output waveguide channels. 
     
     
       16. The photonic coupler of  claim 14 , wherein at least one of the MMI waveguide section or the notched waveguide section includes an inhomogeneous dispersive core material having a pattern selected for adjusting a modal phase between a fundamental mode of propagation and a higher order mode of propagation. 
     
     
       17. The photonic coupler of  claim 14 , wherein the single smooth uninterrupted curvature extends between the notched waveguide sections. 
     
     
       18. The photonic coupler of  claim 12 , further comprising:
 sidewall corrugations disposed along the input waveguide channels and the output waveguide channel. 
 
     
     
       19. The photonic coupler of  claim 18 , wherein the sidewall corrugations comprise opposing pairs of sidewall corrugations on each of the input waveguide channels and the output waveguide channel. 
     
     
       20. The photonic coupler of  claim 12 , wherein the curvilinear sidewalls arc inwards towards the central region of the MMI waveguide section forming a smooth and gradual narrowing of the MMI waveguide at the central region. 
     
     
       21. The photonic coupler of  claim 14 , wherein the single smooth uninterrupted curvature extends from a first notched waveguide section adjacent to the input coupling section to a second notched waveguide section adjacent to the output coupling section.